The present invention relates generally to an illumination source for illuminating a planar surface with a small number of tube-shaped lamps. More particularly, the present invention is directed towards an illumination source for emergency exit signs and emergency exit sign retrofit kits.
An illuminated display sign generally comprises a light source to illuminate a display surface upon which words, symbols, or other indicia are imprinted. Illuminated display signs include a variety of advertising signs, household number display signs, information bearing signs, and a variety of emergency information signs.
As shown in FIG. 1, a common illuminated display sign is an emergency exit sign. Although there are a variety of exit sign configurations, a common prior art emergency exit sign 10 utilizes a rectangular shaped frame, and is commonly known as a xe2x80x9cbox typexe2x80x9d emergency exit sign. Two surfaces 12, 24 of the exit sign 10 are used to display information. Stencil signs have translucent letters and opaque backgrounds. Panel signs have white translucent backgrounds and translucent letters. The display surfaces 12, 24 of emergency exit sign 10 include directional arrows 16 and letters 18 forming the word xe2x80x9cexit.xe2x80x9d
A variety of local regulations, safety organizations, and customs govern the exact size and placement of directional arrows 16 and letters 18 so that there are currently several different size and styles of box-type exit signs installed throughout the United States. The rectangular frame size varies across the United States, but typically is between 8xe2x80x3-to-14xe2x80x3 wide, 7xe2x80x3-to-11xe2x80x3 high, and 1.75xe2x80x3-to-4xe2x80x3 deep. The exit sign letters are typically between 6.0xe2x80x3-to-8xe2x80x3 tall and xc2xexe2x80x3 wide. The directional arrows 16 are typically disposed to the sides of the letters 18, but are also sometimes placed below the letters.
A suitable light source is required to illuminate the arrows 16 and letters 18 of an emergency exit sign 10. FIG. 2 shows a perspective view of the interior of a prior art exit sign with one exterior surface 12 removed for the purpose of illustrating the interior illumination means. Exit signs 210 of the type show are commonly manufactured with two sockets 220 to hold two incandescent bulbs 230. The sockets are typically spaced apart along an upper edge 240 of the sign 210. The incandescent bulbs 230 typically comprise two twenty-watt incandescent lamps.
The cost of operating a single emergency exit sign 210 utilizing incandescent-bulbs 230 can be significant. In addition to the cost of the electricity, the bulbs must be replaced biannually because of the limited operating lifetime of common incandescent bulbs. The average annual operating cost of one emergency exit sign typically averages about $50 per year.
The development of high efficiency light-emitting diodes (LEDs) permits LEDs to be used instead of incandescent bulbs. A single LED has a light output that is highly directional and confined to a narrow cone of emission angles, which makes it difficult to use a small number of LEDs to brightly illuminate an emergency exit sign. Consequently, the light output from a large number of individual LEDs, each disposed at different locations and/or pointed in different directions, is typically needed to brightly illuminate an emergency exit sign. Exit signs utilizing an illumination source comprised of LEDs use about 90% less power than incandescent bulbs and have an output illuminance above the minimum brightness requirement required by Underwriter""s Laboratory(copyright) requirements which can be maintained for a useful lifetime of about 3-10 years. The power output of LEDs depends upon the color (wavelength) of the LED emission. Generally, the most efficient LEDs have a light with a red (long wavelength) color light output, although substantially dimmer LEDs with a green (short wavelength) output are commercially available as well. However, green LEDs with an output power comparable to red LEDs are now commercially available. Because of the monochromatic (single color) output of LEDs, they are best suited for illuminating stencil signs. Currently, about 80% of manufactured red stencil signs are illuminated by LEDs. This is in contrast to the early 1990s, when about 80% of exit signs were illuminated with incandescent lamps.
The standards for brightness and uniformity of illumination of the arrows 16 and letters 18 of an exit sign 10 have become more stringent in recent years in order to address concerns about public safety. A brighter, more uniformly illuminated emergency exit sign is easier to read under a variety of background illumination conditions and/or from a greater distance.
There are currently two separate sets of Underwriter""s Laboratory(copyright) (UL) standards for emergency exit signs under the UL 924 standard which was issued August, 1997. The first set of standards is for new exit signs. New exit signs must have a minimum brightness of 2.5 foot lamberts (FL) as measured along each of twenty different points. The twenty measurement points of the UL 924 standard along different portions of the letters 18 of an emergency exit sign is shown in FIG. 3. There is also a minimum uniformity ratio (UR) requirement in regards to the maximum/minimum intensity of any two of the twenty points. New exit signs must have a maximum UR of 50:1 over the letters 18 and arrows 16, which means that the dimmest of the twenty measured points can have an optical intensity that is at most fifty times lower than the brightest of the twenty points.
A variety of conventional illumination sources may be used to satisfy the UL 924 standard for new exit signs. For example, conventional LED illumination sources used in emergency exit signs typically direct the light output of a large number of individual LEDs to illuminate the letters 18 of an exit sign. Conventional LED illumination source configurations produce an output of about 3 to 8 FL, which diminishes with age to 2.5 FL in a time period of six months-to-ten years.
The second set of UL 924 standards is for retrofit kits, with these standards being more stringent than for new exit signs. Retrofit kits include any kit to replace the standard light source of a conventional exit sign with another light source, such as an energy efficient LED light source. A retrofit kit must be capable of illuminating the letters of a retrofitted exit sign with a minimum brightness at each measurement point in excess of 6 FL and a UR of 20:1. These standards are so stringent that they exceed brightness levels achieved in conventional LED illumination sources (i.e., using common numbers and configurations of LEDs) used in new emergency exit signs.
The problem of designing a retrofit kit to satisfy the UL 924 retrofit standard is exacerbated by the many different sizes and styles of a box-exit sign currently in existence. Under the old retrofit standards, a LED illumination source with a modest number of LEDs could satisfy the illumination requirements of a variety of box-type emergency exit stencil signs. However, under the new retrofit standards, a comparatively large number of LEDs are required to form an illumination source that is bright enough and uniform enough to satisfy the present retrofit standards. Consequently, the cost of an LED retrofit kit is prohibitive when compared to the fewer LEDs needed in a new sign. Several manufacturers have ceased selling LED retrofit kits in favor of selling new exit signs. Unfortunately, the lack of LED retrofit kits may delay the conversion of the estimated 100-to-150 million emergency exit signs in the United States to more energy efficient illumination means. Even if LED illumination sources were suitable for retrofitting stencil-type signs, they are unsuitable for retrofitting panel signs because conventional LEDs have a substantially monochromatic light output. Panel signs require a white-light source to illuminate their translucent letters and white translucent background. Unfortunately, conventional retrofit kits utilizing miniature fluorescent lamps as the illumination source are also unable to satisfy the UL standard for retrofit kits.
Generally, the evolving illumination standards for emergency exit signs makes it difficult to achieve a low-cost, low power consumption, long-life, bright, and uniformly illuminated display surface, particularly in the context of retrofit kits using LEDs. While this is an important concern for emergency exit signs, many of the same considerations also apply to a variety of other illuminated display signs. For example, the illumination of directional pointing arrows, household number signs, and a variety of advertising signs is beneficially improved if the brightness, UR, and energy efficiency is improved. For example, an illuminated display sign to display a home street address number (e.g., xe2x80x9c1010xe2x80x9d) at night is beneficially improved if the brightness and UR is improved so that the address may be read from a greater distance.
What is desired is an improved illumination means for illuminating display signs that overcomes the limitations of conventional sources to achieve improved uniformity and illumination intensity in an energy efficient configuration.
The present invention is directed towards the use of energy efficient miniature lamps, such as cold cathode fluorescent lamps, to illuminate display surfaces, such as those in emergency exit signs, in a substantially uniform manner. The present invention solves the problem of using a small number of miniature tube-shaped lamps to illuminate emergency exit signs, but may be used in other applications as well.
The present invention generally comprises an optical chassis for illuminating a display surface having: a frame; an optical coupler mechanically coupled to said frame having an inner chamber and an outer surface; a tube-shaped lamp with a diameter less than the diameter of the chamber; and a mechanical coupler to suspend said lamp within the center of said chamber while permitting the lamp to flex along its length in response to vibration; wherein the optical characteristics of the optical coupler are selected to alter the trajectory of light rays passing through the optical coupler to improve the uniformity of optical illumination on the planar surface region.
One object of the present invention is an emergency exit sign comprising two optical couplers spaced apart to illuminate the display surfaces of an emergency exit sign.
Another object of the present invention is an emergency exit sign retrofit kit that includes mechanical connectors to lock the optical chassis into pre-existing box-type exit signs. In a preferred embodiment, a ballast compartment is disposed between two optical couplers on an optical chassis, thereby eliminating deleterious shadowing that could occur if the ballast was located outside of the optical chassis.
Still another aspect of the present invention is a thermal design that improves the light output of cold cathode fluorescent lamps by permitting a desirable amount of lamp heating.
Yet still another aspect of the present invention is the use of the optical chassis as an illumination source for path and directional lighting.